Electrophotographic material

ABSTRACT

IN AN ELECTROPHOTOGRAPHIC MATERIAL A PHOTOCONDUCTIVE PREPARATION COMPRISING PHOTOCONDUCTIVE REACTION PRODUCTS OF (I) ONE OR MORE COMPOUNDS OF AT LEAST ONE DIOR POLYFUNCTIONAL ISOCYANATE, AND AT LEAST ONE NON-PHOTOCONDUCTIVE ORGANIC SUBSTANCE, THE PHOTOCONDUCTIVE COMPOUNDS HAVING A PLURALITY OF FREE ISOCYANATE GROUPS LINKED TO AROMATIC OR HETEROCYCLIC RING SYSTEM AND/OR CONJUGATED UNSATURATED ALIPHATIC SYSTEM, AND (II) AT LEAST ONE PIGMENT-LIKE OR CRYSTALLINE COMPOUND SELECTED FROM THE GROUP CONSISTING OF ZINC OXIDE, TITANIUM OXIDE, ZINC SULFIDE, AND CADMIUM SULFIDE.

United States Patent Olfice 3,567,440 Patented Mar. 2, 1971 3,567,440 ELECTROPHOTOGRAPHIC MATERIAL Horst H. J. Kosche, Duren, Germany, assignor to Renker-Belipa GmbI-L, Duren, Germany No Drawing. Filed Mar. 22, 1967, Ser. No. 625,033 Int. Cl. G03g 5/04; H011 15/00 US. Cl. 961.8 3 Claims ABSTRACT OF THE DISCLOSURE In an electrophotographic material a photoconductive preparation comprising photoconductive reaction products of (i) one or more compounds of at least one dior polyfunctional isocyanate, and at least one non-photoconductive organic substance, the photoconductive compounds having a plurality of free isocyanate groups linked to aromatic or heterocyclic ring systems and/or conjugated unsaturated aliphatic systems, and (ii) at least one pigment-like or crystalline compound selected from the group consisting of zinc oxide, titanium oxide, zinc sulfide, and cadmium sulfide.

This invention relates in general to a photoconductive substance and in particular to an electrophotographic material utilizing said photosensitive substance.

It is known in the art to use inorganic substances, like selenium or zinc oxide as photoconductors for photosensitive layers on electrophotographic material. Also certain organic low-molecular-weight substances, like aromatic-substituted axomethines, thiazoles, oxazoles, imidazoles, anthracene, di-fluorenyls, Michlers ketone, and others, have photoconductive properties. In making electrophotographic papers, zinc oxide is used almost exclusively as a dispersion in insulating binders, or together with a mostly low-molecular-weight organic photoconductor. Reaction products of isocyanates with organic compounds containing excessive hydroxyl groups are used among others, as insulating binders. Finally, it is known in the art to use higher-molecular-weight organic components with inherent film-forming properties from the group of vinylpolymers, particularly polyvinyl carbazole, as a photoconductor, and which may be used without any ad ditional binder for producing photoconductive layers.

Photoconductive layers which are formed of a photoconductor made from zinc oxide and a non-photoconductive insulating binder with a specific conductance lower than mho/cm., have the characteristic that they are suitable for image production only after being charged under a negative corona field, in contrast to the layers with organic photoconductors. When test-charging such zinc oxide binder layers under a positive corona field it is impossible to obtain a usable electrophotographic image after exposure, even when using a toner system which would correspond to the positive charge.

Photoconductive layers made of organic photoconductors and insulating binders exhibit such high internal resistance that, when using paper as a layer support means, no light sensitivity could be obtained comparable to that of zinc oxide papers. Electrophotographic zinc oxide papers differ only slightly in appearance from a chromo or special printing paper. Moreover, organic photoconductive components are generally more expensive than zinc oxide.

The common photoconductive layers which contain zinc oxide and an insulating binder may be only negatively charged. This factor has a disadvantageous effect on electrophotographic materials which are covered by such layers. If, for instance, the commercially available zinc oxide binder papers known as Electrofax are used and a positive copy is to be produced from a negative original copy in one operation, it would be required, after negatively charging and exposing the photoconductive layer, to use a different triboelectric toner system when making a print from a positive original copy. In other words, it would be necessary to keep and maintain two different toner systems in the copying machine, or to change the toner system. Hence, it is obvious that the afore-described requirement hampers and disrupts a smooth, continuous operation, and also leads to frequent pollution of the apparatus and the material by the developing agents. Furthermore, a substantial amount of ozone is formed when a charging takes place under a negative corona field. The ozone has a damaging effect on plastic and particularly organic material, as well as on the health of the operator. It is therefore required in these cases to install additional equipment for continuously removing the ozone from a continuously-operating image-producing device, which equipment in turn renders the devices more expensive. Moreover, exhaust channels would have to be installed in the operating rooms. Therefore, for a continuous operation, these devices can only be installed in a permanent location.

The photoconductive material in accordance with the invention consists substantially of a photoconductive preparation, in the form of a layer without any binder. The photoconductive preparation is totally or partly a reaction product of an organic isocyanate and a pigment-like or crystalline compound, the latter being composed of a metal and an element taken from either the main group V or VI of the Periodic Table. The isocyanate is an organic compound which carries at least one free isocyanate group, preferably of an aromatic or heterocyclic ring system or of a conjugated unsaturated aliphatic system. This organic compound may comprise a reaction product, consisting of at least a dior polyfunctional isocyanate and at least one organic compound. Metallic compounds which are inferior or unsuitable as photoconductors such as titanium dioxide, cadmium sulfide, and zinc sulfide may now be used. Metallic compounds which are good photoconductors, especially zinc oxide, may also be used. Due to the reaction these metallic compounds are converted in such a way as to effect a change in their properties while maintaining their pigment-like properties, and display an ability to be charged under positive, as well as negative, coronas.

It is therefore an object of the invention to provide an electrophotographic material capable of producing images having a high light sensitivity.

It is another object according to the present invention to provide an electrophotographic material which may be deposited on a substrate layer of paper.

It is still a further object according to the present invention to provide an electrophotographic material which when deposited on paper produces images having a high degree of contrast.

It is another object according to the present invention to provide an electrophotographic material which is reliable in producing high contrast images when either a negative or a positive charge is used.

These and other objects according to the invention will become apparent from the following detailed description taken in combination with the acompanying claims.

Photoconductive reaction products obtained by a reaction of such organic compounds which are photoconductive per se and which contain groupings capable of reacting with isocyanates, especially active hydrogen, with organic diisocyanates or polyisocyanates, and with epoxides as possible further reaction components, under enlargement of the molecules, may be used for the reaction with the metal compounds. In many cases higher molecular-weight polyisocyanates are particularly suitable. Photoconductive compounds containing the groups $0,

C- -S and N=O in the photoconductor molecule and being reacted with isocyanates at those groupings by conversion and by enlargement of the molecules may be used to produce such self-adhering photoconductors. The photoconductive reaction products may additionally include monohydroxyl or polyhydroXyl group compounds, amines, amides, sulfhydryls, and/or carboxylic acids as reaction constituents. Also suitable for this purpose are photoconductive reaction products of non-electrophotographic specific organic compounds with preferably aromatic, heterocyclic or conjugated unsaturated aliphatic monoisocyanates, diisocyanates, polyisocyanates, or partially modified polyisocyanates. These reaction constituents produce after the reaction, which occurs under molecular enlargement, at one of the group of active H, =CO, =CS, NO with photoconductors which possess self-adhering properties. The organicreaction constituents which are non-electrophotographic must have free pairs of electrons and at least one substituent which would be suited to enter into a mesomeric reciprocal action with the free pairs of electrons, so as to introduce mesomeric properties to the reaction product. Such substituents are, for instance, Alkyl, Acyl, R, (CH%H),,CN, COOH, COOR, COOCO, CONH CONH-Acyl, --CONHOH, CONHR, CONR COSH, -COSR, CSOH, CSNH CSNH-Acyl,

1SO NH SO NH-Acyl, SO NHR, SO' NR SO H, NH NH-Acyl, NR-Acyl, -NHCONH NRCONH NH-CO-NHR, -NR-CONHR, NHCONR NRCONR NHCSNH NRCS-NH -NHCSNHR, NR-CSNHR, NH-CSNR NR-CSNR NHCNH-NH NH-CNH-NHR, --NHCNH-NR NHOH, NHOR, NHSH, NHSR, NHNH NRNH NHNHR, NRNHR, NHR, -NR =NH, =NOH, =NNH :NNR NCO, NO, NO or a halogen, wherein R is selected from the group consisting of aliphatic residues having up to 12 C atoms, phenyl residues, which may contain one or more CN-, dialkylamino-, NO or halogen groups, and known substituents reactive with isocyanates, which is acyl, aliphatic or aromatic monoor polycarboxylic acid and which may contain one or more dialkylamino-, NO OH-, halogen, or keto groups, and wherein n is one of the integers 1, 2, or 3. These substituents have a mesomeric reciprocal effect with the free pairs of electrons of those organic compounds which are non-photoconductive per se. If they are capable of reacting with isocyanates, they may be present in the novel reaction product in the form of groups reacted with the isocyanate constituents, so that the mesomeric effect thereof can be increased further. Finally, these photoconductive conversion products may also include additional reaction constituents like aliphatic monovalent or polyvalent alcohols, aliphatic amino alcohols, methylol ureas, methylolurethane, or aliphatic monobasic or polybasic carboxylic acids, aminocarboxylic acids, or hydroXycarboxylic acids.

The self-adhering photoconductors have molecular groupings which in one molecule provide effective adherence as well as electrophotographic properties. This also permits the production of photoconductive layers having superior adherence capability to supporting matetrials without the need for utilizing insulating binders. As far as can be seen, self-adhering photoconductors which can be reacted with metallic compounds to produce the novel photoconductive layers should contain at least one free non-converted isocyanate group in the molecule in order to be suitable. The non-converted isocyanate group is preferably contained in an aromatic, heterocyclic, or conjugated unsaturated system. Each molecule of a self-adhering photoconductor should contain at least one free isocyanate group. Generally the amount of the free isocyanate groups is 3-30, and preferably 515 mol percent, based on the self-adhering photoconductor.

Due to their easy accessibility, aromatic diisocyanates or polyisocyanates are preferred as the isocyanate constituents for producing the free isocyanate groups containing self-adhering photoconductors. Modified polyisocyanates may also be used and are produced, for example, by the reaction of diisocyanates or polyisocyanates with preferably aliphatic compounds containing active hydrogen. Examples of these compounds are dialcohols or polyalcohols. These modified isocyanates must contain at least two free isocyanate groups. Said free isocyanate groups must be linked to an aromatic, heterocyclic, or conjugated aliphatic system. Modified isocyanates which contain one or more urethane groups in one ring system are especially valuable. Heterocyclic or mixed aromatic heterocyclic diisocyanates or polyisocyanates may be used for forming the self-adhering conductors containing free isocyanate groups. The self-adhering conductor may also be formed by modification with other reactive compounds, especially aliphatic. For making modified isocyanates such diisocyanates or polyisocyanates are preferably used, the isocyanate groups of which show different reaction capabilities. For the production of self-adhering photoconductors containing free isocyanate groups in the molecule, such organic photoconductors or specific organic compounds are preferably used which permit a controlled reaction with isocyanates. At best, those reactive groups or substituents which transfer only one active hydrogen atom to the reaction constituent should be used. If the reaction constituent contains a plurality of active hydrogen atoms, the reactive groups should be selected in such a manner that they show considerable differences in their reaction conditions with respect to the isocyanate. For example, secondary amino groups can be reached with isocyanates without including the phenolic OH-groups in the reaction process. For this purpose, it is useful to convert amino groups into alkylamino-, arylaminoor acylaminogroups before the reaction process. Heterocyclic compounds are substituted in a manner analogous to aromatic compounds, or active hydrogen atoms at the ring system are used for the reaction with the isocyanates.

In any event, a three-dimensional cross-linking should be prevented. The organic photoconductive or non-photoconductive constituents which already contain groupings reactive with isocyanates, and the isocyanate constituent are suitably reacted into a self-adhering photoconductor containing free isocyanate groups in such a manner that the grouping NH-CO-- formed by the conversion of one isocyanate group having active hydrogen, does not participate to a substantial amount in the further reaction with isocyanates. 'I'he self-adhering photoconductors which are produced in this manner and contain free isocyanate groups react together with the metallic pigments into the novel grafted photoconductors, which are also self-adhering.

To make the novel metal-containing grafted photoconductor, the aforementioned self-adhering photoconductor, containing the free isocyanate groups, i reacted with suitable metallic compounds (such as zinc oxide), preferably in an inert solvent. When the reaction is carried out at room temperature, in a vibration or ball mill for example, the process becomes completed only in a few days. It is suggested therefore, that the conversion process be carried out at an increased temperature, preferably in the range of 70l30 C. Generally, when such high temperatures are applied to the inert solution, an effective dispersion aggregate is added. Depending on the nature of the free isocyanate group containing self-adhering photoconductor, e.g., the reaction with ZnO will be completed within 1-2 hours, at 100 C. One recognizes the completion in that the self-adhering photoconductor containing the free isocyanate groups, and combining the ZnO, solidifies into a gel-like or rubber-like substance with the solvent occluded.

After the solvents are removed, this conversion product forms a solid substance which can be pulverized into small pieces. It will swell into a sticky gel in a solvent. In this state, the product may be used for making the photocon-.

ductive layer.

It is also possible to use the reaction product directly in a rfinely dispersed form for making the photoconductive layer, with the possible addition of further organic solvents. It has been found that it is not necessary to carry out the conversion process to the gel-like state, but that the conversion process can be stopped short of reaching the gel-like state. In this case, a partial conversion product is obtained which is still paste-like and provides substantially evenly disposed and smooth-surfaced photoconductive layers. The necessary conversion to the final state can be reached either by drying at elevated temperatures or by storing the product for a few days at room temperature.

Grafted photoconductors can only be split by a chemical reaction. The quantity ratio or the constituents which are used for the conversion process may vary in a wide range. Since the metallic compounds are pigments in the form of granules or crystals, the proportion of metal can be increased far above the stoichiometric ratio with respect to the isocyanate groups without removing the valuable properties of the novel photoconductor. The photoconductor may contain, for example, free isocyanate groups in the molecule, and may be converted with a multiple of the Weight quantity of zinc oxide without reducing its positive charging capability. However, it is a prerequisite that the metallic compounds are present in crystal or lattice structure and are solid bodies before being converted into grafted photoconductors. Experiments showed that 10 to 10 isocyanate groups of the organic compounds are grafted onto zinc oxide granules with a diameter of 2l0 microns. The grafted photoconductors or layers may be sensitized in a known manner. Moreover, an additional quantity of the metallic compounds may be introduced in a non-converted state. The sensitizers generally used in halide-silver photography may be also used for this process. Acid-base or redox-indicators are also effective sensitizers. Sensitizers which combine with the metallic compounds adsorbitively or chemically are particularly valuable. Preferably, the free acid of the dye salt is used for fixing it onto the metallic compound of the photoconductor. Sensitizers found particularly suitable are fluorescein, eosin derivatives of quercetin, rhodamines, sulfophthalines, acridines, thiazines, and tryphenylmethane dyes as well as polymethine dyes, especially cyanine, neocyanine and polycarbocyanine dyes. Although the novel photoconductive layers have a high light-sensitivity and a broad usability, it may be desirable or essential to combine the novel, metallic compounds containing self-adhering photoconductors with other organic or inorganic photoconductors, or with pigments which are not effective as photoconductors for specific applications. As already mentioned above, the novel self-adhering photoconductors have a good adhering capability on a plurality of different supporting materials, making it possible to use the supporting material for making the photoconductive layers without a bonding agent. However, it is possible in specific cases to combine the novel metal-containing grafted photoconductors with binders, or to add plasticisers. It is also possible to make the novel photoconductor selfsupporting.

Preferably, water and ion-containing papers, transparent or transparentized plastic foils and fiber non-Wovens or fabrics are particularly suited as supporting materials for the photoconductive layer, provided they have a higher conductivity than the photoconductive layer.

Furthermore, metal foils, papers which are coated with by vapor deposition or laminating metals, as well as metal stencils and paper stencils used in offset-printing are suitable as supporting materials. The photoconductive layers are formed on the aforementioned supporting materials by means of machines, or any other known technique or method. If desired, an intermediary layer may be provided on the supporting material.

Watery colloids such as starch or cellulose ether, gelatine, caseinates, water-soluble higher-molecular-weight carbohydrates, such as alginates, cellulose glycolates or alkyl-celluloses, polyvinyl alcohol, polyvinyl pyrrolidone, oopolymers of vinyl ether and vinyl pyrrolidone, and others may be used as intermediate layers. Also usable for this purpose are the so called chromo layers or barytic compounds.

Furthermore, it is possible to use the novel photoconductive layers, instead of the already known photoconductive layers, for printing master stencils particularly for lithographic work. In this case it would be possible to make the hydrophobic photoconductive layer hydrophilic at the image-free areas by suitable substances.

To produce images, the electrophotographic material is either negatively or positively charged. In order to keep the adverse effect of the reaction by-product ozone as low as possible, the electrophotographic material is preferably positively charged when positive reproductions are produced from positive copies in a copying apparatus, since generally and quantitively, the positive copies are used more often than the negative copies. The electrophotographic material is charged negatively onlywhen a negative copy is used to make a positive image. In this case, as already mentioned, a positive image may be produced from negative as well as positive copies, with the same triboelectric developer. After the image has been dried it may be fixed by heating or by contacting its surface with solvent vapors so that it cannot be rubbed off. When liquid developers are used, only the liquid medium of the developer has to be removed. Experimental tests have shown that the common triboelectric developers used in electrophotography may also be used for printing stencils.

It was an unexpected surprise to discover that the photoconductive layers which are made from the novel grafted photoconductive layers may be charged under a negative as well as a positive corona. In other words, the novel photoconductive layers act completely dilferent from the hitherto known photoconductive layers made from crystalline zinc oxide in a binder having insulating properties. The novel photoconductive layers act, on one hand, like organic photoconductors, while on the other hand, they maintain the valuable properties of zinc oxide-type photoconductive layers. 'Ihe novel grafted photoconductive layer is not known in the prior art and constitutes an important forward step in the progress of photoconduc tive techniques.

From the aforegoing it can be seen that there are no defined stoichiometric relationships in the above described cases. The size of the surface of the inorganic pigmentlike photoconductors, the number of the gaps or grafting places in the lattice, the steric accessibility of the isocyanate groups of the organic photoconductor, as well as covering the surface of the metallic compound with said groups, the metallic compound surface being converted by forming active hydrogen with, for example, water, carbon dioxide, ammonia or amines, becomes particularly important.

Without limiting the invention to a specific theory of the new properties of the novel photoconductor, which substantially advances the art of electrophotography, it is to be assumed that the organic constituents are grafted, by reaction with the isocyanate groups, onto the surface of the pigment granules of the inorganic metallic compounds in the specific order on their lattice structure,

by a chemical bond. It has been found that metallic compounds which carry water of a different binding energy in an amount smaller than the stoichiometric proportion are particularly easy to convert. Hence, it can be assumed that metallic oxides partially convert into hydroxides, and metallic sulfides convert partially into sulfhydrides. Further, metal atoms may be replaced in the lattice by hydrogen atoms of the H 0. Groups containing active hydrogen and covering the surface of the metallic compound are reactive with isocyanates. Hence they furnish attaching points when grafted with a self-adhering photoconductor the grafting occurs by conversion of the isocyanate group. The function of the oxygen is not quite clear as yet, but it is to be assumed that it effects a binding action.

A further advantage of novel photoconductive layers containing metal compounds consists in the fact that small quantities of water which may penetrate into the photoconductive layer are readily eliminated. There are always small quantities of non-converted isocyanate groups present in the photoconductors. These groups are converted by a further isocyanate reaction with water, which generally originates from the atmospheric humidity, forming carbamic acid or derivatives generated by subsequent isocyanate reaction. Hence, the photoconductive layer remains water-free and ion-free until a saturation point is reached. The storage potentials of the charged photoconductive layers are very high, the storage time is very long, and the sharpness of the contours is extremely clear. Any existing conversion products of the isocyanates with water does not impair the quality of the image. Grafted photoconductors have the characteristic to move in one direction in the electric field Without being sep arated into their individual constituents. This behavior is proof of the high binding stability of the chemical compound of the grafted pigment-like photoconductor.

To form the graft connections between the organic molecules and the inorganic molecules, adjuvants may be utilized. These adjuvants change in part the character of the metallic compound surface or increase the reaction capability thereof. Adjuvants may consist of small quantities of water, water and carbon dioxide, hydrogen sulfide, and ammonia. However, a reaction can be carried out without any of the aforementioned adjuvants.

In view of the aforegoing, the novel photoconductor consists substantially of a metallic compound in the form of granules such as zinc oxide, zinc sulfide, or titanium oxide, which may be converted into a highly reactive condition at its surface by means of adjuvants. A simultaneous or alternative effect is that said metallic compound is capable of reacting with reactive organic compounds due to surplus lattice energy which may be generated by lattice defects at its surface. This reaction binds the organic compound onto the metal compound, the surface of which is permanently and at least partially covered by the organic compound. A chelate-forming process is also possible.

These grafted photoconductors differ in their effects completely from photoconductive metal compounds. The grafted photoconductors barely differ in appearance from mixtures of metal compounds and resins and have a dual action from being electrically charged, i.e. the photoconductors are chargeable under a positive and/or a negative corona. This characteristic renders the grafted photoconductors particularly valuable. They also have the capability to migrate as a unit during electrophoresis and even in a liquid medium. Hence they are particularly suitable for the electrostatic production of photoconductive layers. The present invention will be more clearly described from the following examples:

EXAMPLE 1 A quantity of 262.5 grams of a 75% by weight solution in ethyl acetate of a modified triisocyanate which contains 3 free isocyanate groups in the molecule and has been produced by reaction of 3 moles of 2.4 or 2.6-toluylenediisocyanate with 1 mole trimethylolpropane, and cleaned by means of molecular distillation. The commercial product Desmodur L, from Bayer 'Leverkusen, Federal Republic of Germany, may be used.

To this solution, a quantity of 49.5 grams of ethyl- (B-hydroxyethyl)aniline, dissolved in 150 cm. of cyclohexanone, is added. To make the self-adhering photoconductor containing free isocyanate groups, this solution is converted by stirring for 50 minutes at a temperature of C.

To test its electrophotographic effectiveness, the formed self-adhering photoconductor is coated on an aluminum sheet having an electro-brightened layer of 24 a thickness and dried at C. so that the photoconductive layer has athickness of about 0.006 mm. This test material is charged under a negative corona of 10 kv., exposed under positive original with a high-pressure mercury vapor lamp for 10 seconds, and developed with a triboelectric toner such as Graph-O-Fax Toner 39/50 and glass beads. The result is a high contrast clear print of the original.

To make the novel self-adhering grafted photoconductor which contains metallic compounds, 250 g. of commercially-available zinc oxide Florence Green No. B, dispersed in 400 cm. methyl ethyl ketone, are added, and the mixture is reacted under reflux, and by boiling and stirring at 95 C.

After '60 minutes, the reaction process is stopped, before the material reaches a gel-like state. The product is finely pulverized in a ball mill for about 24 hours. The preparation having good spreading properties is mechanically coated onto a 60 g. cellulose paper in an amount of 60 g./In. (on a dry basis). It is subsequently dried in a hot air stream. The white photoconductive layer formed thereby adheres firmly to the supporting material.

The fresh electrophotographic material can be used for print production only after being negatively charged. The product is cured by storage for three to four days at room temperature. In its final state, the electrophotographic material can be charged positively as well as negatively.

For direct image production, the electrophotographic material is charged under a positive corona of 10 kv. and exposed under a positive original with either an ultraviolet fluorescent tube at of a second, or with an electronic flash. Subsequently, the electrophotographic material is developed with a negative developer, such as commercially-available Xerox Toner 12, and glass beads. A positive image with a ood contrast is obtained from the original. The image is fixed by heating the material with an infra-red lamp.

To make a positive print from a negative, the electrophotographic material is charged under a negative 10 kv. corona and exposed and developed with the aforementioned toner system, as above. A positive image from the original is obtained having a good contrast. The fixation is done in the same manner as previously described, or by applying trichlorethylene vapors.

EXAMPLE 2 To demonstrate the technical progress of the electrophotographic materials of the present invention, over those known in the art, the followin electrophotographic materials will be compared.

(A) An electrophotographic material which has a photoconductor layer consisting of zinc oxide and silicon resin on a supporting paper material, which was produced in accordance with an article published by Radio Corporation of America, LB 1059, on Dec. 31, 1956.

(B) An electrophotographic paper which contains zinc oxide in binders having insulating properties, and presumably sensitizers. This material was shown by Kalle -A.G., Wiesbaden-Biebrich, at the industrial fair at Hannover, West Germany, in May, 1962.

(C) An electrophotographic material produced in accordance with Exam-pie 1.

(1) Samples A, B, and C were commonly charged under a 10 kv. negative corona field and exposed under a positive photographic line original for of a second with ultra-violet incandescent lights. The samples were then developed in the dark room with a direct toner consisting of the commercially available Graph-O-Fax Toner 39/50 (manufactured by the Philip Hunt Company), and glass beads. In all cases positive copies wtih very good contrasts were obtained.

(2) The same electrophotographic materials as used in Example 1 were charged under a 10 kv. positive corona field and exposed under a negative photographic line original for of a second with ultra-violet fluorescent tubes, and were developed with the same triboelectric developer as described under Example 1. Samples A and B did not provide a usable image. Sample C provided a positive copy of the negative original with good contrast.

(3) The same electrophotographic materials used in Example 1 were charged under a positive corona field with 10 kv. and exposed under a positive line photographic original for of a second with ultra-violet fluorescent tubes. The samples were then developed on a toner which reacts to positive charges, such as Xerox Toner 12, containing glass beads. Samples A and B did not provide usable prints. However, Sample C provided a positive print of the original with good contrast.

(4) The same electrophotographic materials as used in Example 1 were charged under a 1 kv. positive corona and exposed under a negative photographic original copy for of a second with ultra-violet fluorescent tubes. The samples were then developed with a toner repelled by positive charges, such as Graph-O-Fax Toner 39/50, and glass beads. Samples A and B did not provide a usable print. Sample C provided a positive print of the negative original with good contrast.

(5) The same electrophotographic materials as used in Example 1 were charged under a negative kv. corona and exposed and developed as in Example 3. Samples A, B, and C resulted in positive prints of the original copy. From this comparison, it can be seen that a reversed copy with Samples A and B could only be obtained when the photoconductive layer was negatively charged and the developer was changed. The novel electrophotographic material, however, can be used universally.

EXAMPLE 3 A solution of 196 g. of a commercial admixture of alpha trimethylolpropane-tris-N-(3-isocyanato-4-methylphenyl) carbamic acid ester and alpha-trimethylolpropane tris N (3-isocyanato-2-methylphenyl)-carbamic acid ester in 100 g. cyclohexanone and 65 g. ethyl acetate were mixed at room temperature with a solution of 49.5 g. N ethyl (beta-hydroxye'thyl)-aniline in 120 g. cyclohexanone. In order to react this admixture it was heated to 120 C. within ten minutes under stirring and kept at this temperature under partial reflux for about ten to fifteen minutes.

A pretreated pulverized dispersion with granules as fine as 520 microns, consisting of'780 g. zinc oxide and 500 g. methylethylketone (which may contain electrophotographic or halogen-silver photographic sensitizers) was mixed With the aforementioned dissolved reaction product, and was further converted for one hour at temperatures of 90100 C. under vigorous stirring. The reaction mixture was then immediately cooled down to room temperature. In order to obtain a uniform particle size, the product is ground to an average fineness of grain between 10 and 20 microns. Further sensitizers may be added. Two parts by volume of the aforementioned dispersion are diluted with one part by volume of methylethylketone and coated by means of a suitable paper-coating machine onto paper suitable for electrophotographic purposes, in such a way that the electrophotographic layer weighs between 10 and 40 g./m. and preferably between and g./m. After the coating operation, the layer is dried in a stream of hot air. The electrophotographic material produced in the above-described manner becomes light sensitive, after being charged under a positive or negative corona. Reproductions can be made subsequently with oppositely poled corona fields on the same sheet of material. All known triboelectric developers may be used for making prints.

An electrophotographic copying paper with an electrophotographic layer of 14 to 18 g./m. on a cellulose paper of 65 g./m. made in accordance with the aforementioned example, is negatively charged under a negative corona of 12 kv. It is then exposed under a positive original and developed with a triboelectric toner system con sisting of a dispersion of dyed plastic resin particles in a liquid hydrocarbon or a liquid halogen hydrocarbon. The triboelectric developer may also consist of dyed plastic particles and pretreated or non-pretreated glass beads, or iron powder. The result is a positive print of the original which has a high resolution and reproduces the unexposed areas in black uniformly and substantially without any edge effect.

The same electrophotographic material, and if desired, the same sheet of material as above-described, was charged under a positive corona of 12 kv. and exposed under a negative line original. Thereafter, the print was developed with the same triboelectric developer as described before. The result was a good contrast and high resolution positive copy of the negative original.

EXAMPLE 4 A quantity of 17.5 g. of a triurethane with three free isocyanate groups at the aryl, made of 3 moles 2, (or 5 )-4- toluene diisocyanate and 1 mole trimethylolpropane as a 75% solution in ethylacetate (available in the trade as Desmodur L, made by Farbenfabriken Bayer AG., Leverkusen, BRD.), with 3.7 g. 3-hydroxydiphenylamine and 25 cc. cyclohexanone were heated under reflux for ten minutes at a temperature of 135 C. Thereafter, 40 g. of zinc oxide (Florence green), that is 298% with respect to the organic photoconductor, and 40cc. of methylethylketone were added and heated under reflux for thirty minutes at C. The reaction mixture is ground on a vibrating mill for two hours. A photoconductive layer made of this product yielded a good electrographic image when negatively or positively charged and developed.

EXAMPLE 5 A quantity of 17.5 g. Desmodur L dissolved 75% by weigh in ethylacetate, with 3.4 g. 4-hydroxydiphenyl and 25 cc. cyclohexanone, were heated under reflux for about thirty minutes at 135 C. Thereafter, 40 g. of zinc oxide (Florence green) and 40 cc. of methylethylketone were added and the mixture was heated under stirring and reflux for twenty minutes at a temperature of 85 C. A layer made of this material yielded a good electrophotographic image when positively and negatively charged and developed.

EXAMPLE 6 A quantity of 17.5 g. of Desmodur L, dissolved 75% by weight in ethylacetate, with 3.94 g. of 2,3-dihydroxybenzoic acid-beta-hydroxyethylamide and 25 cc. of cyclohexanone, were heated under reflux at C. for fifteen minutes. Subsequently, this solution was admixed with 40 g. of Zinc oxide (Florence green) and 60 cc. of methylethylketone and was further heated under reflux at 85 C. for about fifteen minutes. The mixture was ground in a vibrating mill for two hours. A layer made of this material yielded a good electrophotographic image when being negatively or positively charged and developed.

EXAMPLE 7 A quantity of 17.5 g. of Desmodur L, dissolved 75 by weight in ethylacetate, with 5 g. of a p-toluene-N- methylsulfonamide resin, such as Santolite MHD of Monsanto Chemical Company, St. Louis, Mo., U.S.A., were heated under reflux at C. for about ten minutes. After adding 40 g. of zinc oxide (Florence green) and 40 cc. of methylethylketone, the reaction admixture was heated to 85 C. under stirring for thirty minutes further, and then ground in a vibrating mill for one hour. A layer made of this material provided a good electrophotographic image when negatively or positively charged and developed.

EXAMPLE 8 A quantity of 17.5 g. of Desmodur L, dissolved 75% by weight in ethylacetate, with 3.28 g. of 4-dimethylaminobenzaldoxim and 25 cc. of cyclohexanone were heated under reflux at 130 C. for about ten minutes. Thereafter, 40 g. of zinc oxide (Florence green) and 6 cc. of methylethylketone were added. The mixture was then heated to 85 C. under stirring for another fifteen minutes. A layer made of this material provided an electrophotographic image when negatively or positively charged and developed.

EXAMPLE 9 A quantity of 17.5 g. of Desmodur L, dissolved 75% by weight in ethylacetate, and 3.3 g. of S-diethylaminophenol and 25 cc. of cyclohexanone are heated under reflux at 135 C. for about ten minutes. Thereafter, 40 g. of Zinc oxide (Florence green) and 40 cc. of methylethylketone are added. The mixture is heated to 85 C. for fifteen minutes and is finally ground in a vibrating mill. A layer made of this material provided an electrophotographic image when negatively or positively charged and developed.

EXAMPLE 10 A quantity of 17.5 Desmodur L, dissolved 75% by weight in ethyl acetate, 29 g. of S-hydroxyquinoline and 25 cc. of cyclohexanone were heated under reflux to 130 C. for ten minutes. After adding 40 g. of zinc oxide (Florence green) and 40 cc. of methylethylketone, the reaction mixture was heated to 85 C. under-stirring for another fifteen minutes and finally ground in a vibrating mill for about one hour. A layer made of this material provided an electrophotographic image when negatively or positively charged and developed.

EXAMPLE 11 A quantity of 17.5 g. of Desmodur L, dissolved 75% by weight in ethyl acetate, 2.8 g. of 4-nitroaniline and 25 cc. of cyclohexanone were heated under reflux at 135 C. for about ten minutes. Thereafter, 40 g. of zinc oxide (Florence green) and 40 cc. of methylethylketone were added. The mixture was heated to 85 C. under stirring for another rfifteen minutes, and finally ground in a vibrating mill for one hour. A layer made of this material provided an electrophotographic image when negatively or positively charged and developed.

EXAMPLE 12 A quantity of 40 g. of zinc oxide (Florence green), 40 cc. of methylethylketone, 17.5 g. Desmodur L, dissolved 75% by weight in ethyl acetate, and 25 cc. of cyclohexanone were mixed and ground in a vibrating mill without prior heating, and finally coated onto a supporting paper material. The coated paper material was then dried in the following manner:

(a) In an air stream (b) In a dry chamber at 100 C., for about one minute, or

(c) In a dry chamber at 100 C., for about four minutes.

After positively charging the coated paper material, the following test results were obtained:

Test 1.No image. Test 2.A very vague image. Test 3.--An image of somewhat higher density than in 12 Test 2. The image did not improve with a higher temperature and longer drying period.

All test samples provided usable electrophotographic images after being negatively charged.

The mixture which contained zinc oxide, and which had not been heated, was then heated under reflux and stirred at C. for about ten minutes. Thereafter, it was pulverized for a short period of time. When this materal was positively or negatively charged, very good electrophotographic images were obtained. As a comparison, a mixture made with active zinc oxide (Bayer) only provided a very weak image when the material was negatively charged.

EXAMPLE 13 A quantity of 15 g. of Desmodur L, with .10 g. TiO and 5 cc. of cyclohexanone were boiled under reflux for about fifteen minutes. Thereafter, the solution Was diluted with 10 cc. of methylethylketone and pulverized in a ball mill. Thereafter, the product was coated onto a paper material. An electrophotographic image was obtained when this layer was both positively or negatively charged.

EXAMPLE 14 A quantity of 196.5 g. of Desmodur L, 24.75 g. of ethyl-beta-hydroxyethylaniline, 216.0 g. of cyclohexanone and 65.0 g. of ethylacetate are heated under reflux to about 130 C. for about twenty minutes. g. of this reaction admixture were admixed with 100 g. of cadmiumsulfide and 10-0 g. of acetone and heated under reflux with stirring at 65 C. The total mixture was ground in a vibrating mill over night. A layer made of this material provided a good electrophotographic image when both negatively or positively charged.

EXAMPLE 15 A quantity of 20 g. of a Desmodur condensate (same as in Example 14), 20 g. of zinc sulfide and .10 cc. of methylethylketone were mixed and heated under reflux with stirring at 85 C. for fifteen minutes and then pulverized for a short period of time. A layer made of this material provided a good electrophotographic image when both negatively or positively charged.

While only a few embodiments of the present invention have been shown and described, it Will be understood that many changes and modifications may be made therein without departing from the spirit and scope of the invention, as defined by the appended claims.

What is claimed is:

1. An electrophotographic composition capable of forming a self-adherent electrophotographic layer and of accepting either a positive or a negative charge, consisting essentially of the reaction product of:

(a) a photoconductive organic isocyanate having at least one free isocyanate group in the molecule linked to an aromatic, heterocyclic, or conjugated aliphatic moiety, and

(b) an organic nonphotoconductive compound containing free electron pairs and having linked to a moiety selected from the group consisting of phenyl, quinoline, and aliphatic containing from 1 to 12 carbon atoms, a substituent reactive with isocyanates selected from the group consisting of amino, dialkylamino, amido, nitro and hydroxy, the reaction product of (a) and (b) having from about 3 to about 30 mol percent free isocyanate groups, based on the self-adhering photoconductor, and

(c) a metal compound selected from the group consisting of zinc oxide, titanium dioxide, zinc sulfide and cadmium sulfide, said metal compound being reacted with said reactants (a) and (b) at a temperature of about 70 C. to about C. for a period of about 1 to 2 hours.

2. The composition of claim 1 in which said photoconductive compound is additionally reacted with a member selected from the group consisting of an aliphatic monovalent alcohol, an aliphatic polyvalent alcohol, an aliphatic amino alcohol, a methylol urea, a methylolurethane, an aliphatic monobasic carboxylic acid, an aliphatic polybasic carboxylic acid, an amino carboxylic acid, and a hydroxycarboxylic acid in an amount such that the resulting product contains at least one free isocyanate group per molecule.

3. The composition of claim 1 wherein said reaction products are formed in the presence of water utilized as a catalyst.

References Cited UNITED STATES PATENTS RICHARD D. LOVERING, Primary Examiner U.S. C1. X.R. 

